Migrate to yarn to install packages without package.json (but keep npm rebuild)

Author: th-ch

.npmrc

@@ -0,0 +1 @@
+engine-strict=true

.travis.yml

@@ -31,9 +31,9 @@ script:
         -v ~/.cache/electron:/root/.cache/electron \
         -v ~/.cache/electron-builder:/root/.cache/electron-builder \
         electronuserland/builder \
-        /bin/bash -c "npm install && npm run release:linux"
+        /bin/bash -c "yarn && yarn run release:linux"
     else
-      npm run release:mac
+      yarn run release:mac
     fi
 before_cache:
   - rm -rf $HOME/.cache/electron-builder

appveyor.yml

@@ -12,9 +12,9 @@ init:
 
 install:
   - ps: Install-Product node 8 x64
-  - npm install
+  - yarn
 
 build_script:
-  - npm run release:win
+  - yarn run release:win
 
 test: off